In a housing of electronic device such as a mobile phone, a method appropriately selected from materials of resins or metals is used in consideration of various factors such as decoration properties, scratch resistance, workability, and cost. In recent years, glass which has not been used in the related art has been attempted to be used as a material of a housing (Patent Document 1). According to Patent Document 1, in the electronic device such as a mobile phone, it is possible to exhibit a distinctive decorative effect with a transparency feeling by forming a main body of the housing with glass.
Electronic device includes a display device such as a liquid crystal panel on the outer surface of the device. Such a display device tends to have high definition and high luminance, and a backlight serving as a light source tends to have high luminance in accordance with the tendency. Light from the light source is radiated to the display device side and reaches the rear surface of the housing externally mounted through multiple reflections in the inside of the device in some cases.
In addition, even in a case of an organic EL (Electro-Luminescence) display which does not need a light source, similarly, leakage of light from a light emitting element is concerned. When a metal is used as a material of a housing, such a problem is not caused. However, when glass having transparency as described above is used there may be the case where light from the light source is transmitted through the housing and then recognized from the outside of the device. Accordingly, when glass is used for the housing, light shielding means such as a coating film for allowing glass to have a shielding property with respect to visible light (hereinafter, referred to as a shielding property) is formed on the rear surface of the glass.
As described above, in accordance with high luminance of the light source in the display device, it is necessary to form a thick film or a film formed of a plurality of layers as a coating film in order to form the coating film with a sufficient shielding property on the rear surface (device side) of glass, and this results in increasing the number of steps and the cost.
Further, in a case where the coating film is not uniformly formed, there is a concern that light is transmitted through only a portion whose coating film is thin and the appearance of the device may be impaired, for example, such that the housing is recognized to be locally bright. For example, in a concave housing, it is necessary to form a uniform film on the entire surface on a concave surface side. However, a step of uniformly forming a coating film having a sufficient shielding property on a concave surface is complicated and this results in increasing the cost.
Particularly, in a case where a housing whose appearance exhibits white is obtained, a method of forming a white coating film layer on at least one surface of transparent glass as described above may be used. However, since a white coating material has high translucency, a sufficient shielding property cannot be obtained even when the white coating film layer is made thick.
Consequently, a black coating film layer having a high shielding property is laminated on a white coating film layer, but it is necessary to make the white coating film layer thick to the extent that the black coating film layer is not recognized. In this manner, when a housing having a high shielding property, which exhibits white using a white coating material, is obtained, there is a problem that the cost thereof is extremely high.
Further, in electronic device which can be used for a mobile phone or the like, a housing is needed to have high strength in consideration of fracture due to impact from a fall during use and contact scratch due to use over a long period of time. Accordingly, in the related art, in order to improve scratch resistance of glass or a glass substrate, the glass is chemically strengthened to form a compressive stress layer on the surface thereof so that the scratch resistance is improved.